Torii Kiyonaga (Japanese: 鳥居 清長; 1752 – June 28, 1815) was a Japanese ukiyo-e artist of the Torii school. Originally Sekiguchi Shinsuke, the son of an Edo bookseller, he took on Torii Kiyonaga as an art name. Although not biologically related to the Torii family, he became head of the group after the death of his adoptive father and teacher Torii Kiyomitsu.
The master Kiyomitsu died in 1785; since his son died young, and Kiyotsune, Kiyonaga's senior, was a less promising artist, Kiyonaga was the obvious choice to succeed Kiyomitsu to leadership of the Torii school. However, he delayed this for two years, likely devoting time to his bijin-ga and realizing the immense responsibility that would fall on his shoulders once he took over the school. Thus, in 1787, he began organizing the production of kabuki signboards and the like, which the school held a near monopoly on. He also began to train Kiyomitsu's grandson, Torii Kiyomine, who was to succeed him.
Source: Wikipedia, "Torii Kiyonaga", available under the CC-BY-SA License.